Lasers have been shown to be effective and convenient surgical tools. Among the variety of possible surgical lasers the ArF excimer laser has been found to be the best choice for producing precise cuts during tissue removal in a gaseous environment without collateral damage to the surrounding tissue layers (C. A. Puliafito, R. F.
Steinert, T. F. Deutch, F. Hillencamp, E. F. Dehm, C. M. Adler, Ophthalmol. 92, 741(1985); S. L. Jacques, D. J. McAulitte, I. H. Blank and J. A. Parrish, J. Inv. Derm. 88, 88(1987); J. Marshall, S. Trokel, S. Rothery and R. Krueger, British J. Ophthalmol. 70, 487(1986). This considerable advantage of the ArF excimer laser is based on a photochemical, rather than thermal, mechanism of the tissue removal (R. Srinivasan, P. E. Dyer, B., Braven, Lasers Surg. Med. 6, 514(1987)). The energy of the 193 nm photon is sufficient for breaking almost all chemical bonds in biological compounds. This fast photochemical reaction followed by fast tissue removal prevents heat deposition and other side effects caused by other lasers. Up to now all surgical applications of the ArF excimer laser were based on the treatment of tissue surface in an air environment. Excellent results were obtained, for example, in refractive surgery (F. A. L'Esperance, J. W. Warner, William B. Telfair, P. R. Roger, C. A. Martin, Arch. ophtalmol., 107, 131(1989)) and skin treatment (S. L. Jacques, D. J. McAulitte, I. H. Blank and J. A. Parrish, J. Inv. Derm. 88, 88(1987)).
During the last few years new methods based on fiber optic delivery systems have been developed for laser angioplasty (T. G. van Leeuwen, L. van Erven, J. H. Meertence, M. Motamedi, M. J. Post, C. Burst, J.Am. Coll. Cardiol., 19, 1610(1992); T. Tomary, H. J. Geschwind, G. Boussignac, F. Lange, S. J. Tank, Am. Hear J., 123, 8861992)), bone and cartilage cutting and drilling (M. Dressel, R. Jahn, W. New and K. H. Jungbluth Lasers Surg. Med., 11, 569(1991)), and other surgical applications. These methods are simple, convenient and allow the delivery of a laser beam to the required position in a liquid environment. The laser wavelength ranges being transmitted through these fibers were mainly associated with the spectral range of the fiber's transmittance, which is the mid IR, visible and near UV and thus, these wavelengths were used for tissue cutting even though such wavelengths are not the optimum for tissue removal. In all such tissue removal applications with these laser wavelengths different measures of thermal injury or shock waves caused side effects in the surroundings of the lesion. The best results were obtained with the 308 nm excimer laser (T. G. van Leeuwen, L. van Erven, J. H. Meertence, M. Motamedi, J. J. Post, C. Burst, J.Am. Coll. Cardiol., 19, 1610(1992); T. Tomary, H. J. Geschwind, G. Boussignac, F. Lange, S. J. Tank, Am. Heart J., 123 8861992)). But even in this case the mechanism of laser/tissue interaction was shown to be thermal. All attempts to effectively deliver the ArF excimer laser beam through quartz fibers failed because of both the non-linear absorption at high intensities and induced color centers formation at this wavelength. As a result, at high radiation intensities and for multiple pulses quartz fibers were shown to become almost nontransparent (M. Dressel, R. Jahn, W. Neu and K.-H. Jungbluth Lasers Surg. Med., 11, 569(1991)).
Until recently only one method of the ArF laser delivery into a liquid environment was developed (A. Lewis and D. Palanker U.S. Pat. No. 5,288,288). The laser beam was guided through a hollow glass tapered micropipette, in which a gas was introduced at a pressure equal to the capillary force of the liquid at the pipette exit. The micropipette served at the same time as a beam guide, a concentrator and an aperture. This method allowed the drilling of precise and reproducible holes in the zona pellucida of oocytes for enhancement of sperm penetration (D. Palanker, S. Ohad, A. Lewis, A., Simon. J. Shenkar, S. Penchas and N. Layfer, Lasers Surg. Med., 11, 580(1991)). For this application the diameter of the tapered tip was about 8 microns and a low energy fluence was applied. For larger tips and a high energy fluence the method of static gas pressure is not effective for maintenance of an air/liquid boundary at the exit of the tip.
The instrument we have devised overcomes all of the problems of ArF laser delivery to a tissue in a highly absorbing liquid environment and allows the cutting of materials with high speed and high precision without observable heat injury.